The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow its significance to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should not be construed as an admission that such art is widely known or forms part of common general knowledge in the field.
Thickeners are known as a means of separating suspended pulps. They are commonly used in the field of mineral processing and extraction, as well as in other industries.
Known thickeners typically include a thickening tank and a feedwell. The feedwell includes a chamber having an inlet for receiving feed slurry and an outlet in fluid communication with the tank. In use, flocculation takes place in the tank, whereby pulp of higher relative density tends to settle towards the bottom of the tank, forming a bed of thickened pulp, and dilute liquor of lower relative density is thereby displaced towards the top of the tank.
The feedwell is configured to reduce the turbulence of the incoming feed slurry, to allow flocculants to be mixed into the liquid, and to allow sufficient residence time for reaction between flocculants and reagents, before the treated liquid is discharged into the thicken tank. The configuration of the feedwell is typically also intended to promote uniform distribution of slurry flowing from its outlet into the thickening tank.
Feed slurry concentration affects the rate of floc formation, and the dosage rate of flocculant required to achieve optimum separation. It also affects thickener performance in terms of overflow clarity and underflow density versus flocculant consumption. Accordingly, the feed slurry entering the feedwell frequently requires dilution in order to achieve an optimum result.
Existing technologies achieve feed slurry dilution by several methods. Some methods involve pumping supernatant or new liquid into the feed stream. Relatively newer methods, however, use liquid from within the thickening tank to dilute the feed stream. These newer methods typically employ mechanisms of differential density or momentum transfer to move the liquid from the thickening tank into the feed stream.
All of these existing methods have disadvantages. Those utilising pumps require considerable pipework and electrical power to transfer the diluting liquid. Conversely, the internal systems, which use differential density or momentum transfer mechanisms, are relatively simpler and require little to no electrical power, but lack means to precisely control dilution under all operating conditions.
It is an object of the invention to overcome or substantially ameliorate one or more of the deficiencies of the prior art, or at least to provide a useful alternative.